A tag reading device reads article information stored in a wireless tag (e.g., a RFID tag) which is attached to an article or articles. The tag reading device can perform inventory tracking or inventory loading and unloading management based on the article information that is read. There are mobile types and stationary (fixed) types of tag reading devices. For example, a tag reading device of the stationary type has a plurality of flat antennas installed on a gate and reads information from a wireless tag attached to the articles passing through the gate.
In such a tag reading device with a gate, a distance from an antenna to an article can be long, and it thus may be necessary to increase the intensity of radio waves emitted by the antenna so as to reliably read the wireless tags. On one hand, if the intensity is increased, there is a possibility that wireless tags will be inadvertently read from beyond an intended reading region. Therefore, it becomes necessary to keep other articles with tags away from the intended reading region or to occupy a wider work area, with countermeasures to limit inadvertent reading. On the other hand, in a case where the emitted radio wave intensity is decreased, there is a potential problem with missed readings occurring with respect to wireless tags on articles tightly packed together within boxes or the like.
Accordingly, in inventory tracking and/or loading and unloading management applications, there is a demand for a device which can reliably read article information from wireless tags attached to a plurality of articles without unnecessarily increasing the intensity of the radio wave emitted from the antenna.